Strip pickling apparatus and saturable reactor control therefor



1953 DUNNEGAN, JR, ETAL I 2,651,009

T. STRIP PICKLING APPARATUS AND SATURABLE REACTOR CONTROL THEREFOR Filed Oct. 24, 1949 2 Sheets-Sheet l MAGNETIC IFIER [YWVC-DTYCCTS: Ted Dunnegganyrg Hugh IV]. QQIQC;

Thei 1" Atterney.

1, 1953 T DUNNEGAN, JR. ETAL 1,

STRIP P'ICKLING APPARATUS AND SATURABLE REACTOR CONTROL. THEREFOR Filed Oct. 24, 1949 2 Sheets-Sheet 2 MAGNETIC Z8 AMPLIFIER VARIABLE Invcentmwas Ted Durmaggasn Jr :P Hugh M. G /3 m by y/fiz Their" Attorney;

Patented Dec. 1, 1953 STRIP PICKLING APPARATUS AND SATU- RABLE REACTOR CONTROL THEREFOR Ted Dunnegan, Jr.,

and Hugh M. Ogle, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application October 24, 1949, Serial No. 123,296

'7 Claims.

This invention relates to a saturable reactor type proximity and control system for regulating the positioning of ferromagnetic material.

This application is a continuation-in-part of our application Serial Number 48,893, filed September 11, 194.8 (now abandoned), and assigned to the same assignee as the present application.

A particular object of the invention is to provide an improved control system to regulate the immersion of continuously moving steel strip in a pickling bath. Although described in terms of this particular use, it will be appreciated that the system, in whole or in part, can be used in other similar applications.

Other objects and advantages of the invention 1 will become apparent as the description proceeds The features of the invention which are believed to be novel and patentable are pointed out in the claims which form a part of this specification. For a better understanding of the invention, reference is made in the following descri tion to the accompanying drawing, in which Fig. 1 is a schematic diagram of a complete control system associated with a pickling bath; Fig. 2 is a schematic diagram of the preferred proximity gauge used in the system shown in Fig. 1; Fig. 3 is a schematic diagram of a modified form of the proximity gauge; Fig. i is a schematic diagram of another modified form of the proximity gauge; and Fig. 5 is a schematic diagram showing modifications of the complete control system. Where the same or an identical part appears in more than one figure of the drawing, it is always repr sented by the same reference number.

Referring now to Fig. l, in a steel strip processing operation, steel strip 1 is drawn from takeup loop 2 through rollers 3 and 4. Roller 4 is driven by a variable-speed Il-C. motor 5. From rollers 3 and the strip is fed into pickling tank 6 which contains a pickling solution I. Tank 6 may be made of bricks, as illustrated, or other suitable material to withstand the corrosive action of the pickling solution.

Strip l is drawn from the pickling tank, through rollers 8, and wound upon reel 9 by variable-speed D.-C. motor iii. Motors 5 and Eli are supplied with variable direct current through connections H, which may, for example, be connected to a Ward-Leonard system which controls the speed at which the steel strip is processed. Rheostats i2 and I3 are provided so that motors 5 and I9 may be adjusted to run at approximately the desired speeds.

It is desirable that strip 1 be immersed as far as possible in the pickling solution without dragging the bottom of the tank 6. Usually an average clearance of about six inches between the strip and the bottom of the tank is considered desirable. It is evident that if the strip drops too close to the bottom of the tank, it can be restored to the correct position by slightly decreasing the speed of motor 5; and that if strip l is pulled up too far above the bottom of the tank, it can be restored to its correct position by slightly increasing the speed of motor 5. These variations in the speed of motor 5 can be effected by having a booster generator I i electrically connected in series with motor 5, as shown, to raise or lower the net voltage applied to the motor, as required. Generator H has a field winding l5 adapted to be externally excited. Any suitable means, for example an electric motor, not shown, may be employed to drive the rotor of generator Hi.

In control systems previously used, the depth of immersion of strip l in the pickling solution has been gauged by a mechanical dancer arm riding upon the strip. Because of the highly corrosive nature of the pickling solution, the life of mechanical parts in contact with the solution is short, and resulting mechanical failures have been numerous and troublesome. By providing a saturable reactor type proximity gauge as hereinafter described, contact of gauge parts with the corrosive pickling solution is eliminated.

Preferably the proximity gauge is embedded in the floor of the pickling tank, as shown in Fig. 1. A plate 66 of lead, or other non-magnetic, corrosion-resistant material, is used to protect the gauge from the corrosive solution. Since, as hereinafter explained, only direct magnetic flux passes through the lead plate, there are no losses due to induced eddy currents as would be the case if alternating flux passed through the plate.

The proximity gauge includes a two-legged saturable magnetic element ll. Preferably element ll is about twice as long as the distance from the gauge to strip l. Thus, if element i! is embedded three inches below the floor of tank d and strip I is to clear the floor by six inches, element ll may be about eighteen inches long. A first winding I8 is provided about both legs of element l1, and second and third windings i9 and 20 are provided about respective ones of the two legs. A battery 2| and a rheostat 222 are connected to energize Winding I3 with an adjustable value of direct current.

Rectifiers 23 are respectively connected in series with windings I9 and 28. A transformer having a primary 25 adapted to be energized with alternating current through connections 2&3, has

a center-tapped secondary ill. The two halves of secondary are respectively connected across the two sets of seri-es-connected windings. Thus, two alternating volts 3 in. phase opposition are provided across wirand its associated rectifier across v. and its rectifier, respectively.

A magnetic amplifier 23 has a signal winding 29 connected in series with both sets of series connected rectifiers and windings, as shown. second signal winding 30, or bias winding, is energized from a constant D.-C. source through connections 3|. The value of the bias current flowing through winding 30 can be adjusted. by rheostat 32.

An amplidyne generator 33 has a field winding 34 connected to the output of magnetic amplifier 2B. A second field winding 35 is energized. by a bias current, the value of which may be adjusted by rheostat 35. The amplidyne genera tor rotor is driven by any suitable means, for e:- ample an electric motor, not shown. The output of amplidyne generator is connected to energize field winding of booster generator l4.

Refer now to Fig. which shows the proximity gauge and its magnetic flux paths. Two alter hating voltages in phase opposition are applied across winding l9 and its series-connected rectifier, and across winding 2i! and its series-corn nected rectifier, respectively. Because of the rectifying action of rectifiers Z3, pulsating direct current flows through windings l9 and These pulsating currents have alternating components which produce alternating magnetic nux along the path indicated by broken line This alternating fillX is substantially confined within the saturable magnetic element, and thus follows What is herein referred to as a confined magnetic circuit.

Direct current through winding iii and direct components of current through windings {El and produce direct magnetic flux which travels from left to right through element IT and re-- turns through the air or the pickling solution and through any magnetic material in proximity to element ll. Such fll. paths are illustrated by broken lines til. Since this flux is not con fined to element H, and since the paths which it follows vary depending upon the proximity of ferromagnetic materials, the direct flux follows what is herein referred to as an unconfined magnetic circuit.

The direct magnetic flux passing through element l1 partially staurates this ele-. ent. When a ferromagnetic material, such steel strip i, is moved into proximity to the gauge, the reluctance of the unconfined magnetic circuit reduced and hence the amount of direct through element H is increased. Since most oi the reluctance of the circuit is in its non-magnetic portion, variations in thickness of strip i produce little effect, and proximity alone determines the reluctance. An increase in direct increases the saturation of element H and thereby reduces the reactance of windings l9 and it. This permits more curernt to flow through these windings. The increased current has a larger direct component which still further increases the direct flux. Thus, the gauge has a regenerative action which provides very high sensit. vity. If high sensitivity is not required, the rectifiers may be omitted.

It is, of course, not necessary that the entire element 31 be saturated by the direct flux. There may be, for example, saturable portions in 4. each leg of element H, and the remainder of the element may remain unsaturated.

Refer again to Fig. 1. Suppose strip 1 drops nearer the floor of tank ii; this increases the current through windings is and 20, and hence the current through signal winding oi the magnetic amplifier. This in turn increases the current through field winding 3'3 of the aniplidyne generator, which then energizes field winding 55 of the boos Jer generator with a polarity such that booster generator 44 generates a voltage opposing the voltage applied to motor Thus, the net voltage applied to rnotor "5 is reduced, and that motor runs at a slower s This tends to restore strip 5 to its proper immersion depth. Conversely, if strip is too far away from the bottom of tanl: 5, the current through winding 29 is reduced and motor 5 is cause-:1 to run at a higher speed until strip i is restored to its proper position.

Initial adjustments for the desired immersion depth of strip l are made by adjusting rheostats 22, 3E, and 38. Rheostat 22. should be adjusted to give a degree of saturation of element ll \vhic will provide a relatively large change in inductance of windings It and 2t for small changes in reluctance of the unconfined magnetic circuit. Ptheostat adjusted to a good operat ing point magnetic amplifier 23. Rheostat 3.53 is then adjusted to balance the system at the desired depth.

If desired, arnineter 31 can be connected in s ies with winding 29 and may be calibrated to in: cute directly in appropriate units the immersion. depth of strip Reer now to Fig. 3, which shows a modificaticn of the proximity gauge. A capacitor 40 is connected in parallel with winding 20 as shown, has a value such that winding 2c is tuned somewhat below resonance at the frequency of alternating current employed. As element ll approaches saturation and the reactance of winding it! decreases, winding Eli and capacitor 40 approach parallel resonance and the impedance presented by the parallel circuit increases. Thus, current through the right-hand rectifier 23 decreases whi e current through the left-hand rectifier increases. These currents flow through opposits halves of center-tapped resistor t! and pro. e voltage across the resistor which is proportional to the difference in value of the two currents. Winding 2c is connected in parallel with resistor 4i and is energized by amount proportional to the voltage across the resistor.

Refer now to 4, which is a schematic diagrarnv of anothe modification of the proximity gauge. This modification is similar to the illustrated in Fig. 2, except for the means for pr viding direct magnetic fiux through the unconfined circuit. Instead of a winding linking the unconfined circuit, permanent magnets are used. The permanent magnets may be small bar magnets l'l and 43, arranged at respective ends of element ii, as shown, with their polarities aiding to provide direct magnetic flux, represented by broken lines id, through the unconfined circuit. Otherwise, operation is the same as in the 2 circuit.

Somewhat better operation can be obtained if a separate motor is used to draw the steel strip from the pickling tank, instead of relying entirely on the motor which drives reel 8. A further improvement in operation is obtained by additional control means for automatically maintaining substantial equality between the speed at which strip enters the pickling tank and the speed at which it emerges, so that only small errors need correction by the proximity gauge control. An arrangement of this type is shown in Fig. 5. Referring now to this figure, motor I drives reel as hereinbefore explained. Another motor 45 drives roller 8' to draw the steel strip from the pickling tank at a substantially constant speed. Motor is supplied with current through connections ll, and a rheostat 46 is provided for adjusting the speed of this motor to a desired value.

Motors iii and 45 automatically divide their load, and consequently no special means to maintain a proper speed relation between the two is necessary. If motor 45 should tend to run faster than required for it to keep up with motor It, motor 45 picks up a larger portion of the load, which tends to reduce the speed of motor 45 and increase that of motor It, until the correct speed relation is restored.

Two small D.-C. generators 41 and 48 are mechanically coupled to motors and 45, respectively. Generators 4! and 48 are of the type commonly called D.-C. tachometer generators which provide direct current proportional in value to the speed at which the generator is driven. Generators 41 and 48 are connected to supply current through magnetic amplifier signal windings 49 and 50, respectively. The current through winding 49 acts upon the control system to decrease the speed of motor 5, while current through winding 58 acts to increase the speed of motor 5. Rheostats 5| and 52 may be provided, in series with the tachometer generators as shown, for adjusting the currents through windings i9 and 56 to equality when the speed of strip entering the pickling tank equals the speed of strip leaving the tank. If motor 5 should momentarily run faster than motor 45, generator 47 supplies more current through winding 49 than generator 48 supplies through winding 56. This tends to reduce the speed of motor 5, and restore the speed equality. But if strip l becomes too close, or not close enough, to the bottom of the tank, the proximity gauge operates as hereinbefore described to correct the error. The complete system described is unusually stable and free of any tendency to hunt excessively.

It will be appreciated that other modifications and arrangements which may occur to those skilled in the art, such as feeding the strip into the pickling tank at constant speed and using the proximity gauge to control the withdrawal rate for regulating immersion depth, are within the scope of this invention.

Having described the principle of this invention and the best mode in which we have contemplated applying that principle, we wish it to be understood that the apparatus described is illustrtaive only, and that other means can be employed without departing from the true scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A proximity gauge for ferromagnetic materials, comprising a confined magnetic circuit and an unconfined magnetic circuit the magnetic element of each of said magnetic circuits consisting of the same saturable element, means to provide direct magnetic through the unconfined circuit, a winding linking the confined circuit and a portion only of the unconfined circuit, a rectifier connected in series with said winding, connections to apply alternating voltage across the series connected winding and rectifier, and apparatus responsive to the value of current through said winding.

2. A proximity gauge for ferromagnetic materials, comprising a confined magnetic circuit and an unconfined magnetic circuit both the magnetic element of each of said magnetic circuits consisting of t e same saturable element, first and second windings linking the unconfined circuit and the confined circuit respectively, connections for energizing the first winding with direct current, a rectifier connected in series with the second winding, connections to apply an alternating voltage across the series-connected second winding and rectifier, and apparatus responsive to the value of current through the second winding.

3. A proximity gauge for ferromagnetic materials, comprising a two-legged saturable magnetic element, a first winding around both legs of element connected for energizing the first winding with direct current, second and third windings around respective ones of the two legs, rectifiers connected in series with the second and third windings respectively, connections to apply two alternating voltages in phase opposition across the respective sets of series-connected rectifiers and windings, and apparatus responsive to the value of currents through the second and third windings.

i. A proximity gauge for ferromagnetic ma terials, comprising a two-legged saturable magnetic element, a first winding about both legs of said element, connections for energizing the first winding with direct current, second and third windings around respective ones of the two legs, a capacitor connected in parallel with said third winding, rectiners connected in series with the second and third windings respectively, connections to apply two alternating voltages in phase opposition across the respective sets of seriesconnected rectifiers and windings, and apparatus responsive to a diilerence in value between the direct currents through the second and third windings respectively.

5. A control system for a D.-C. motor which regulates the position of ferromagnetic material, comprising a booster generator electrically connected in series with the D.-C. motor and having a field winding adapted for external excitation, a confined magnetic circuit and an unconfined magnetic circuit both including a common saturable element and positioned in proximity to the ferromagnetic material the position of which is controlled, first and second windings linking the unconfined circuit and the confined circuit respectively, connections for energizing the first winding with direct current, connections for energizing the second winding with current having alternating components, and a current amplifier connected to provide through the field winding of said booster generator 9, current dependent in value upon the current through said second wind ing.

6. In apparatus for pickling steel strip, includmg a pickling tank, means to draw strip from the tank, and. means including a variable-speed D.C. motor to feed strip into the tank, an improved control system comprising a bocster generator electrically connected in series with the D.-C. motor and having a field winding adapted for external excitation, a two-legged saturable magnetic element embedded in the floor of the pickling tank, a first winding around both legs of said element, connections, for energizing the first winding with an adjustable valueof .clirect current, second and third windings around respective ones of the two legs, rectifiers connectedin series with the second and thirdwindings respec tively, connections to :apply twoalternating vo1tages in phase opposition across the respective sets of series-connected rectifiers and windings, a magnetic amplifier having a. signal Winding connected in series with ,bothsets of series-connected rectifier-s. and windings, the depth of immersion of the strip controlling the values of the currents flowing in said sets and thevoltage supplied-to said signai Winding amplidyne having 1 a field winding connected. across the output of themagnetic amplifier and having its output connected to the field winding of said booster generator.

'7. In a system for controlling the depth of immersion or" strip material in a tank havingv electric motors for feeding such material into the tanl: for iirithtirawing material from thetank respectively, the combination of: a boostergenerator connected in series with one of such motors for varying the relative speeds of such'motors, means including a magneticamplifier fox-controlling the voltage generated by said booster HUGH M. 'OGLE.

References Cited in thefile of this patent I UNITED STATES PATENTS Number Name Date 2.1153154 La Pierre i- Slept. 1, 1935 "2226275 Abbott et a1 Dec. 24', 1940 2,329,021 Walsh Sept. 7, 1943 23121146 Hoare Dec. 3, 1946 2,512,372 'Pakala June 20, 1950 

